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The domain of the present invention is lighting, encompassing the technical uses of lighting for photographic purposes, including motion picture, video and digital imaging. It also encompasses the areas of critical viewing, both for task and ambient light, and lighting design for commercial or residential space, as well as light for general use when the user is cognizant of lighting qualities even if not technically proficient in their measurement and control.
Introduction—People face the problem of needing to augment available ambient light with additional light sources or lamps. They may also need to create light where none exists. People with technical proficiency in lighting have strategies and means to provide this needed light in a manner that is technically and aesthetically appropriate to the situation. This includes people such as those involved in creating images through photographic means (including still and motion picture photography with film, video or digital means), or involved in lighting design, or those professionally evaluating images or materials. The added light should be sensible in terms of matching or complementing available light, or with the characteristics that would be expected if ambient or natural lighting existed. Any new source will be selected and if necessary, modified, to suit parameters such as the direction, quality, intensity and color temperature as well as color rendering of the existing or expected light. If this is not accomplished, then the work, imaging or viewing is compromised. This requires a moderate to high level of technical proficiency to enact successfully, and is often time consuming.
There is a large population without technical proficiency in lighting, but who are observant or sensitive to their lighting environment. For example: anyone who has dimmed a light or shut off a fluorescent light or lit candles to suit a mood; or who has preferred the light of daylight fluorescents at work during daytime, and their incandescent desk lamp when working late at night. More recently, this would include anyone who has turned off a Light Emitted Diode (LED) desk light at night because the light is too “cold” for night reading. There are a number of lamp types that are designed for this population to suit one particular time of day or unvarying subjective quality of light, thus requiring no particular technical proficiency to use.
The method of intentionally using and blending light sources with more than one color temperature has been in existence since the advent of color photography, and exploited for centuries before that in paintings. An example image could include a person sitting in a room with a lantern, and daylight streaming in a window. The lantern light is warmer, the daylight cooler. These sources have different color temperatures and the intermediate, blended values might be seen on the subject's face. A camera would register and record all of these varying color temperatures. The resulting image would be a type ubiquitous in modern motion pictures and still photos, with warm and cool light plus blended and neutral tones seen on the subject.
Color temperature is objectively measured in degrees Kelvin (° K.), with a color meter or through other photometric means. Film is supplied as either daylight or tungsten balance, with any variation from the two established norms compensated for by use of calibrated filtration. In video and digital imaging systems, the term “white balance” is used to refer to the system tracking of color temperature to render a white or neutral color correctly, without amber or blue bias. The human mind does this automatically, and novices are often surprised that light they perceive as neutral is recorded as deep amber or bright blue.
Pertinent technical issues of lighting are described in further detail in the attached Appendix.
Because most sources do not match the full spectral output of a “black body radiator”, measurement of their output is labeled as degrees Kelvin CCT, or correlated color temperature. A single lamp with multiple bulbs (sources) of differing CCT value may exhibit a blended CCT. An example is a fluorescent luminaire designed for motion picture use that can house combinations of individual tubes with either daylight CCT or tungsten/halogen CCT values. In a lamp that houses four tubes, CCT can be adjusted in one quarter increments of intermediate values between daylight and tungsten CCT.
This concept has been demonstrated in many other lighting devices that house more than one individual source. Intermediate CCT values are obtainable by using individual sources within the lamp of differing CCT, and if these source types are dimmable (as most are) that by reciprocal dimming a range of intermediate CCT values can be obtained. This has been shown for fluorescent lighting by Ravi et al in U.S. Pat. No. 5,952,343 from 1998, wherein two fluorescent lights of differing CCT, within the same housing, are provided with varying power to vary the blended total CCT output of the device. It has also been shown with MR16 halogen sources using warm and cool CCT bulbs (commercially available employing dichroic filtration) arranged in an array and separately dimmed according to CCT value.
There is an existing technology to provide a light source with user variable CCT through an entirely different approach. According to the teachings of You, et al. in U.S. Pat. No. 7,201,494, this involves using LEDs with narrow spectral output, which combined in Red, Green and Blue arrays can be tightly controlled to produce white light with sufficiently predictable CCT and high CRI for use in these critical viewing or photographic applications. There are a number of inventions with similar approach, differing in details of use, components, construction or application. These inventions and products involve blending of single wavelength output LED light, whether just RGB primaries or including secondary colors such as cyan, magenta and yellow, rather than blending full spectrum white LED light of differing CCT values.
This type of RGB blending, or RGB plus secondaries blending, is consistent in conceptual approach with that of computer and video monitors, which create colors and white through mixture. The tracking of white light values through this approach is illustrated through the CIE chromaticity chart with blackbody locus (see FIG. 4). When control over white light is the desired function, only an extremely small subset of the total gamut is of concern, that of the blackbody locus and its immediate surroundings. When RGB blending is used to track these specific coordinates, the vast majority of total available gamut is ignored, and if that gamut is exploited, it is outside the area of concern for white lighting. Maintaining white light output with RGB blending involves high precision sensors and feedback loops to arrive at and maintain specified coordinate values automatically, whether through electronics, microprocessor control or other means.
Regarding Lenses, Reflectors and Diffusers—The common lens functions are that of condensing, collimating and making more efficient the utilization of the source, for a brighter, more uniform and directional beam. In addition, lenses commonly control, sometimes in conjunction with reflectors and diffusers, the beam angle and dispersion of the light output. As permanent components of a lamp, they provide either fixed or variable means to control intensity and beam characteristics.
Reflectors are often built into lamps with non-directional sources. This includes glowing filaments that emit in all directions, and fluorescent tubes. The reflectors assist the efficiency of a lamp by re-directing source output that is emitted away from the primary direction of the desired lamp beam. Reflectors come in a vast range from mirrored surfaces to simple white painted surfaces. Higher efficiency correlates to more specular, “harder” quality, while a “softer” quality typically correlates to lower efficiency. With most sources types, the reflected light is combined with the source emissions prior to exiting through a lens and/or diffuser.
Diffusers are usually secondary to lenses and reflectors, and serve to create a more even source. They also can increase the effective radiating area of a source, either for direct viewing such as an illuminated panel, or for softening the boundary of shadows on a subject. Diffusers are sometimes permanent parts of lamps, and sometimes temporarily attached to suit varying needs.
Technical luminaires that include both reflectors and lenses have been used in theatrical and photographic industries for generations. Fresnel lamps and ellipsoidal luminaries are two common types with integral reflector and lens used in conjunction with the emitting source. Both types feature knobs or cranks for manual user adjustment or focusing of the projected beam. There are common sources that employ permanent reflectors such as the PAR (parabolic aluminized reflector) bulb. Often, the replaceable bulb is a sealed unit combining filament and reflector. In the case of LEDs, a primary lens in usually intrinsic to the unit, with secondary lenses and/or reflectors added as needed.
In theatrical and stage use, multiple luminaries are often controlled through dimmer boards to mix and match the total light output, color or other variables available by manipulating individual units or the total set. Modern commercial and residential lighting design usually includes multiple sources, each with a desired set of characteristics, which are then controlled through various means, including dimmers, to provide users with a lighting environment that can be tailored to task or mood.
Regarding Thermal Management—High power, white LEDs are unlike incandescent sources in a critical area. Incandescent sources heat a filament in order to radiate visible light. It is quite normal for them to radiate more heat then light and is not detrimental, just inefficient. Tungsten/halogen sources must reach a very high temperature to enact the “halogen cycle” that regenerates the filament and maintains efficiency. High temperature operation is needed. In contrast, LEDs are electronics that must be kept relatively cool for long life and proper functioning. Since high power LEDs generate heat commensurate with their output, they require thermal management to be used in functional lamps. The luminous flux (brightness) of these sources will drop when their junction temperature goes above a threshold value and will continue to drop as temperature increases. Life expectancy drops in similar manner. At higher than rated temperatures, these products incur increased rates of failure, including the possibility of catastrophic failure, wherein the individual unit is irrevocably destroyed, with the potential for subsequent cascading failure across multiple units within an array. This sensitivity to self-generated temperature also makes them unlike fluorescent sources or other gas discharge sources, which typically require no special thermal management. Thus, a high output LEDs carry both general and specific recommendations regarding thermal management from manufacturers.
Commercial Availability of Components—Recent generations of high power white LEDs are available with a predictable CCT range and sufficiently high CRI to be usable in professional photographic applications and for critical viewing applications at office or home or in commercial use. These come from a variety of commercial sources such as Phillips, Osram and others.
Heat sinks, both as individual components and as lengths of extrusion profile, and as custom assemblies are commonly available. In the majority of cases, the material in use is aluminum or anodized aluminum. General LED lamp design recommendations suggest such things as using the entire housing as a heat sink, or incorporating any heat sinks into the total structure of the lamp.
Secondary lenses and diffusing products now exist specifically for high power white LED sources. These are typically made of PMMA (polymethylmethacrylate) and are available in a variety of beam angles and levels of efficiency, with and without holders to mount to specific LED packages. They are available with beam shaping characteristics comparable to existing fixtures of traditional type, and with novel characteristics originating with LED sources.
Constant current drivers and/or ballast products are available for use with AC or DC input and output current or incorporating transformers for use with AC main (line) current. Models exist that permit dimming or varying LED intensity through means such as potentiometers or pulse width modulation. These are specifically designed for high power LEDs, and circuit diagrams for LED array configurations including switching and dimming are provided.
There is an existing technology that involves blending narrow or single wavelength RGB sources with white and orange sources to achieve variable color temperature, according to the teachings of Rahm, et al. (U.S. Pat. No. 6,636,003). That prior art differs from the present invention in that it does not use wide spectrum white LED sources as the exclusive means of generating user variable CCT value white light. It also differs in the areas of integral lensing, integral thermal management and specification of manually responsive controls.
Other existing technologies—There is an existing technology that involves blending of “different colors” of LED light through the use of light guides, to achieve white light with a reliable CCT value, according to the teachings of Ward, et al. (U.S. Pat. No. 7,063,449). That prior art differs from the present invention in that it uses light guides. It also differs in that it does not have high power, high CRI white LEDs of specific CCT value as the only sources, which are then blended to achieve intermediate values. It also differs in the areas of integral lensing with optional diffusers, integral thermal management and specification of manually responsive controls.
There is prior art to combine a white LED of high CCT with an LED source that is warm/amber, to permanently create a blended white light source with a single, uniform, unvarying CCT, according to the teachings of Huang, et al. (U.S. Pat. No. 6,395,564). This is specifically to create a synthesis of white LED light plus warm LED source to form a single intermediate white source. This differs from the method of the present invention in many ways: it does not address variable CCT or intensity, integral lensing, integral thermal management or manually responsive controls.
There is prior art relating to color temperature variations in an LED lamp through the use of dimming, according to the teachings of Melanson, et al. (U.S. Pat. No. 7,288,902). It is similar to the method of the present invention in that it is dedicated to the control scheme of creating variable CCT through the use of selectively or reciprocally dimming white light LEDs, as opposed to through RGB type blending. It differs from the present invention in that: it specifies use of alternating current for dimming; does not include use of direct current input; does not include integral lensing or optional diffusing elements as part of the lamp in order to create a virtual single source with specific or variable directionality and beam characteristics such as reduced color fringing of shadows; does not specify high power white LED emitter sources with high CRI; does not describe or involve integral thermal management or use of the heat sink(s) as structural mounts for LEDs; and does not specify or include reference to manually responsive controls for direct sensory hand-eye control and “feel” by the user (in contrast, it references setpoint type control, indicative of symbolic, non-real-time control). This prior art further differs from the present invention in that current working embodiments (and future embodiments) of this present invention offers professional users a complete functional lamp that relies only on sensory input to achieve light color and quality to match existing or desired sources, and enables non-technical users to exploit variable color temperature without the need for proficiency in deriving setpoint targets or control schema.
Pohlert, et al., in U.S. Pat. No. 7,163,302, discloses a lighting effects system and includes an arrangement of lamp elements, such as LEDs or other light elements on a panel or frame. The panel may include one or more circuit boards for direct mounting of the lamp elements. Different color lamp elements may be mounted on the panel and, in particular, daylight and tungsten colored lamp elements may be used, with their relative intensity selectively controlled. In particular arrangements shown in that patent (FIGS. 38B, 39 and 40), a panel light comprises one or more rows of surface mount LEDs secured to a mounting surface. The mounting surface may be a circuit board which in may be attached to an outer aluminum frame or other preferably light weight material to provide a structural support for the circuit board. Optional fins on the backside of the frame may assist with heat dissipation. Elsewhere in that application there is shown a lens cap which may act as a focusing lens to direct the light output from an LED in a forward (or other) direction.
Other LED light assemblies, such as those shown in Burkholder, U.S. Pat. No. 7,284,882 include thin, flexible circuit boards with surface mount LEDs and other electronic components that are attached to a metal heat sink, such as by using a layer of thermally conductive adhesive. Vias may be incorporated in the circuit board near attachment pads used to bond the LEDs. These vias provide a conduction path from the back side of the LED carrier through the circuit board and through the thermally conductive adhesive and thus to the heat sink.